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Laser heating

  1. Jun 22, 2007 #1
    I need to heat a sample of biological materal to a certan tempature with a laser. How do I find the right amplitude/wavelength/power to reach the correct tempature?

    (sorry my spelling could be better) ^.^
  2. jcsd
  3. Jun 22, 2007 #2
    Why do you need to use a laser?
  4. Jun 22, 2007 #3
    Personal prefrance....and to see if it will work
  5. Jun 22, 2007 #4


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    First you need to find a wavelength that your sample adsorbs strongly.
    Then you need to find a wavelength that you can generate a reasoanble amount of power at.
    Then you need to know the mass, heat capactiy and cooling rate of the sample to calculate what power you need.

    Odds are you don't want to use a laser unless you need to heat a very small area of a sample without effecting other parts - in which case buy/borrow a medical cauterising laser.
    ps - if it can heat a biological sample then it can heat you, so you probably want to consider some safety aspects, especially if you know nothing about lasers!
  6. Jun 23, 2007 #5
    Well my whole idea was to create a PCR machine that utilized a laser, to alow for smaller sample sizes and a reduction in radiated heat
    Last edited: Jun 23, 2007
  7. Jun 24, 2007 #6
    What advantage does a laser have over an LED, in your application?
  8. Jun 24, 2007 #7


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    I don't have an answer for you, Oober, but I do have a question. I'm familiar (in a layman's way) with PET, CAT, (strangely, no DOG :uhh:), MRI, and etc. devices, but I've never heard of PCR. What is it?
  9. Jun 24, 2007 #8
    For those that don't know their biology/google, http://en.wikipedia.org/wiki/Polymerase_chain_reaction" [Broken] is the usual method of multiplying DNA for any sequencing, and requires a controlled temperature cycle.
    Last edited by a moderator: May 2, 2017
  10. Jun 24, 2007 #9
    My thinking was that I would be able to oscillate the lasers "power" to the required tempatures faster and more effeciantly then convential PCR machines.
    Last edited: Jun 24, 2007
  11. Jun 24, 2007 #10


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    Oscillate the laser's power? What is this?

  12. Jun 24, 2007 #11

    Claude Bile

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    Firstly you need to know the absorption spectrum of your sample. From there it is a matter of selecting a suitable wavelength and power - you are more likely going to be restricted by what wavelengths are commercially available more than anything here.

    Secondly, since, from the sounds of things, you want to not only heat, but maintain the sample at a certain temperature, the size and shape of the sample will be critical here as it will determine the rate of cooling of the sample, which will in turn determine at what point the sample will reach thermal "equilibrium" for a given laser power and wavelength.

    For a simple heating application though, I'm not sure a laser is necessary - other (cheaper) forms of optical sources such as flashlamps or LEDs would do the job just as well. The only tangible advantage a laser gives in this instance is the ability to focus onto a very small spot and deposit energy in a highly controlled manner - it is not clear that this is necessary here.

  13. Jun 25, 2007 #12
    Ok how would i go about doing this with LEDs or some other light source?
  14. Jun 25, 2007 #13
    Ok so oscillate was a bad word choice....^.^
  15. Jun 25, 2007 #14
    You could control the energy input with a "pulse width modulated" and gently focussed LED, but you'll almost certainly require a (non-optical) temperature sensor in thermal contact, so I don't see any sense at all in optical heating.

    If you want "smaller sample sizes and a reduction in radiated heat", the obvious solution is a small and well-insulated conventional PCR machine. For superior efficiency (to radiate less heat), use a solid state heat pump (a small Peltier device or thermocouple), rather than creating new heat (as with a resistive heater, LED, or even less efficient laser).
    Last edited: Jun 25, 2007
  16. Aug 26, 2009 #15
    Dear laser-PCR hopeful-

    Neglecting photochemical or phase transition processes, the energy absorbed by a sample in response to laser irradiation is entirely converted to a rise in temperature. Sample heating of biological targets by laser light has been reported with large varibility.
    [Peterman, E. J. G., F. Gittes, and C. F. Schmidt. 2003. Laser-induced heating in optical traps. Biophysical Journal 84:1308-1316.]

    The primary band overlaps including overtone resonances in water (~950 nm) and RNH2 groups (~1030 nm) with many other absorption bands found throughout the spectrum from 700 nm – 2500 nm.
    [Vogel, A., and V. Venugopalan. 2003. Mechanisms of pulsed laser ablation of biological tissues. Chemical Reviews 103:577-644.]

    I do a lot of PCR (qRT-PCR to be more precise). Laser thermal cycling has been done.
    Start here with a recent paper:
    Nanodroplet real-time PCR system with laser assisted heating
    Kim H, Dixit S, Green CJ, et al.
    OPTICS EXPRESS Volume: 17 Issue: 1 Pages: 218-227 Published: JAN 5 2009

    Peace out yo!
  17. Aug 26, 2009 #16


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    Now I feel kinda stupid. I've heard of polymerase chain reaction, but didn't associate the initials with it. :redface:
    Last edited by a moderator: May 4, 2017
  18. Aug 26, 2009 #17

    Andy Resnick

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    Have you ever used a PCR machine, like the LightCycler? I would be amazed if you could easily improve on this device.
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